1. Field of the Invention
This invention relates to a liquid discharging method typified by an ink jet recording method of discharging liquid droplets, a liquid discharging head typified by an ink jet recording head, a liquid discharging head cartridge and an ink jet recording apparatus.
2. Related Background Art
An ink jet recording method of discharging minutes ink droplets from a nozzle (discharge port) to thereby effect the recording of characters, figures, etc. has been attracting attention as a recording method in an apparatus for effecting recording, such as a printer, a copying apparatus, a facsimile apparatus or a plotter. The ink jet recording method has the excellent advantage that the outputting of highly minute images and high-speed printing are possible. Particularly, a method of producing air bubbles in liquid by an electro-thermal converting member (hereinafter also referred to as the heater) and using this produced bubble pressure, i.e., the so-called bubble jet method, is characterized in that the downsizing of the apparatus and the higher density of image are easy to realize.
Now, the liquid discharged from the nozzle by the bubble pressure is not limited to ink liquid, but it is possible to discharge other liquids. So, herein, a method of discharging not only ink, but generally liquids is called the liquid discharging method, and in the liquid discharging method, a method of discharging ink liquid to a recording medium to thereby effect recording is called the ink jet recording method.
In the field of ink jet recording, the requirement for the coloring of recording is high. As the construction of an ink jet recording apparatus which satisfies the requirement for the coloring, there is adopted, for example, one in which color recording is effected with ink jet recording heads of various colors are arranged in parallel along the scanning direction on a carriage, or one in which color ink jet recording heads comprising ink tanks containing therein yellow, magenta and cyan inks used for color recording and recording heads for discharging these inks, the ink tanks and the recording heads being arranged in parallel so as to make a unit, and a single ink jet recording head for black only are disposed on a carriage and color recording is effected.
FIG. 20 of the accompanying drawings is a schematic cross-sectional view of the ink flow path portion of a recording head of the conventional bubble jet type using an electro-thermal converting member to produce air bubbles to thereby discharge ink liquid droplets. A heater portion 91 is embedded in an ink flow path 92, one end of which communicates with a discharge port 93, and the ink flow path 92 is filled with ink. Heat produced by the heater portion 91 acts on the ink filling the ink flow path 92, whereby the ink on the heater portion 91 causes a sudden state change (bubbling phenomenon) and some of the ink in the ink flow path 92 is discharged and flies from the discharge port 93 to a recording medium, whereby recording is effected. The bubble produced by the heat generation of the heater portion 91 shrinks and disappears when the heating by the heater portion 91 ends, and the ink flow path 92 again becomes filled with ink (the ink refill process).
However, in the conventional recording head as shown in FIG. 20, the bubble produced may become larger than necessary and in such case, much time is required for the disappearance of the bubble. Also, at the same time as the energy during bubbling is transmitted from the heater portion 91 toward the discharge port 93 (in Q direction), the energy is greatly transmitted toward the upstream side (in P direction) which is the ink supply side and therefore, there is the problem to be solved that much time is required for refilling the ink flow path 92 with the ink. A pressure wave propagated to the upstream side with the production of the air bubble is herein called a back wave.
The recording head of such flow path construction as shown in FIG. 20 could coped with the printing speed in the recording apparatus as is conventional, but in the recent recording apparatus wherein higher speed recording is desired, the ink refill time has been not enough for the printing speed and in some cases, the non-discharge of the ink has occurred.
Also, in an ordinary ink jet recording head, a common ink chamber for supplying ink to a plurality of ink flow paths is provided upstream of the flow paths, but when such a back wave is strongly transmitted to the upstream side of the ink, this back wave may be propagated to other ink flow path through the common liquid chamber and may adversely affect the discharged state of the ink in that flow path.
The above-noted facts that much refill time is required and that there is the adverse effect of the back wave have been problems to be solved that generally apply to liquid discharging heads utilizing air bubbles to discharge liquid droplets.
Various propositions have heretofore been made in order to solve such problems. Description will hereinafter be made of propositions made to an ink jet recording head, and it is apparent that the following construction is generally applicable to liquid discharging heads.
For example, as described in Japanese Laid-Open Patent Application No. 55-100169, there is known a construction in which a fluid resistance portion is provided upstream of a heater portion in an ink flow path for generating heat energy. The structure of such ink jet recording head is shown in FIG. 21 of the accompanying drawings. As shown in FIG. 21, ink 904 flows from an inlet opening 903 at one end of an ink flow path 902 into the ink flow path 902 communicating with a discharge port 901 for discharging the ink. Near the discharge port 901 at the other end of the ink flow path 902, a heater 905 for generating heat energy utilized to form air bubbles and discharge the ink is disposed on a wall surface, and a barrier 906 is protrudingly provided on the upstream side (the inlet opening 903 side) of the heater 905 on the wall surface on which this heater 905 is disposed. In such recording head, when an electrical signal is inputted to the heater 905, an air bubble is produced in the ink 904 and by the action thereof, ink droplets 907 are discharged from the discharge port 901 toward a recording medium 908. At the same time, the acting force of the air bubble acts also in the anti-discharging direction (the direction toward the inlet opening 903), but due to the barrier 906 provided in the anti-discharging direction, the fluid resistance in the anti-discharging direction becomes greater than the fluid resistance in the discharging direction, and the acting force of the air bubble is effectively utilized for the discharging of the ink droplets 907.
Also, as a method of preventing the loss of energy toward the upstream side of such a heater, there is disclosed in Japanese Laid-Open Patent Application No. 59-199256 a method of providing, besides discharge energy generating means directly concerned in the discharge, second energy generating means which is not directly concerned in the discharge. By using the second energy generating means, the loss of the energy generated by the discharge energy generating means toward the upstream side is prevented.
Also, in Japanese Laid-Open Patent Application No. 62-240558, there is disclosed a method of providing heating means in a liquid chamber, in addition to the heater arrangement of Japanese Laid-Open Patent Application No. 59-199256.
In Japanese Laid-Open Patent Application No. 63-102945, there is disclosed structure in which discretely from a discharge heater for controlling discharge, second energy generating means is provided so as to be orthogonal to a flow path so that the component in the direction of the flow path width of this second energy generating means may become greater than the flow path width.
Further, Japanese Laid-Open Patent Application No. 63-197652 or Japanese Laid-Open Patent Application No. 63-199972 discloses that a valve mechanism is utilized as a fluid resistance element to prevent the loss of discharge energy. The flow path structure disclosed in these publications is that shown in FIGS. 22A and 22B of the accompanying drawings. In this recording head, an electro-thermal converting member 912 for forming air bubbles is provided on a substrate 911 correspondingly to each ink flow path 913, and one end of each ink flow path 913 is a discharge port 915 and the other end thereof is connected in common to a common liquid chamber 916. A valve mechanism 914 has such an initial position that sticks on the ceiling of the ink flow path 913, is provided upstream of a heat acting area near the electro-thermal converting member 912 (the projection space toward the surface of the electro-thermal converting member) with respect to the direction of flow of ink, and is structured to be opened by a back wave. This recording head is designed to operate the valve mechanism 914 so as to prevent the propagation of the back wave toward the more upstream side, thereby preventing the loss of discharge energy.
Also, there have been proposed a liquid transporting method and apparatus in which the above-described electro-thermal converting member or an electro-mechanical converting member (such as a piezo element) is used as a liquid transporting mechanism and provision is made of a fluid resistance element for suppressing the movement of liquid in the direction opposite to the desired direction of movement of liquid such as the above-described back wave or the like. That is, any apparatus capable of driving liquid in one direction by some mechanism corresponds to the liquid transporting apparatus herein referred to. From the viewpoint of the liquid transporting apparatus, the ink jet recording head can be said to be one which transports liquid from an ink tank toward a discharge port, irrespective of whether an air bubble is produced by the use of an electro-thermal converting member, and discharges the ink from the discharge port at predetermined discharge pressure. For example, an ink jet recording head provided with the valve mechanism described in the above-mentioned Japanese Laid-Open Patent Application No. 63-197652 or Japanese Laid-Open Patent Application No. 63-199972 can also be regarded as one using an electro-thermal converting member as a liquid transporting mechanism, and contriving to control the flow of ink in one direction by a valve mechanism. Likewise, it is also attempted to use a piezo element to realize the flow of liquid in one direction.
However, in a case where a fluid resistance portion is provided as described in Japanese Laid-Open Patent Application No. 55-100169, as compared with a case where it is not provided, when liquid is discharged at a relatively low driving frequency, the influence of the back wave can be prevented to some extent by the action of the barrier (liquid resistance portion) provided in the liquid flow path, as previously described, but when the liquid is discharged at a frequency higher than that, the influence of the back wave from the upper portion of the barrier is unavoidable and refilling is impeded by this barrier and is delayed. Further, there arises the problem that the vibration of liquid in a nozzle cannot be controlled and repeated proper discharge cannot be effected.
Also, the technique described in Japanese Laid-Open Patent Application No. 59-199256, Japanese Laid-Open Patent Application No. 62-240558 and Japanese Laid-Open Patent Application No. 63-102945 provides, besides a heater for the discharge of liquid droplets, a heater for controlling a back wave, and contrives to control the rearward propagation of the back wave by an air bubble produced by the heater for controlling the back wave. In the case of such construction, when it is necessary to sufficiently secure the bubbling pressure of the heater bubbling for the discharge of ink liquid droplets, the bubbling pressure of the heater for controlling the back wave will be overcome by the bubbling pressure for discharge unless the heater for controlling the back wave is made sufficiently large. If the heater for controlling the back wave is made large for the sufficient control of the back wave, the length of the entire liquid flow path will become great, and this gives rise to the problem that there is rather formed an area in which refill becomes slow.
Also, when provision is made of a valve mechanism adapted to be opened by a back wave as described in Japanese Laid-Open Patent Application No. 63-197652 or Japanese Laid-Open Patent Application No. 63-199972, the air bubble for discharge naturally grows also on the upstream side of the liquid flow path, and in the process, the value mechanism disposed in the upper portion of the liquid flow path moves while corresponding to (being led by) the flow of the growing air bubble. That is, most time of the growing process of the air bubble passes until the valve mechanism 914 is opened to its position shown in FIG. 22B. Therefore, there is a case where it is impossible to suppress the back wave which is the original object and sufficiently prevent the loss of discharge energy. Particularly, when such construction is applied to a recording apparatus which discharges liquid at a high driving frequency, the frequency cannot be coped with.